This invention relates to high purity boron pellets, useful as dopants in the manufacture of single crystal, low resistivity, silicon ingots. Such ingots are starting materials for preparation of semiconductor devices. This invention also relates to a process for producing high purity boron in free-flowing, bead-like form.
Current methods for preparing electronic grade crystalline boron for doping, comprise decomposing boron halides in Siemens-type reactors. Operating temperatures are customarily within the range of 1,000.degree. to 1,300.degree. C. Such processes are energy intensive and inefficient, and corrosive by-products are produced. The boron product is in rod-like form.
The boron rods are customarily purified by float-zoning, or a similar technique. Such purifications comprise another energy intensive, high temperature process. After purification, the material is crushed, separated into desired particle sizes, and blended to produce the desired product. Impurities may be introduced during the crushing, size separation, and blending operations. Moreover, these steps have fairly significant yield losses.
Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, Volume IV, Page 65, says in part "Direct thermal decomposition of boron compounds to high purity boron is limited to halides and hydrides. Boron tribromide or triiodide, and boron hydrides (from diborane to decaborane) have been decomposed on a wide variety of substrates ranging from glass to tungsten at temperatures from 800.degree.-1500.degree. C."